This invention relates to a field emission cathode, and more particularly to a field emission cathode suitable for use as an electron source for a fluorescent display device, particularly, a graphic fluorescent display device, as well as an electron source for a light source in the filed of lithography to which a principle of a fluorescent display device is applied.
Various kinds of field emission cathodes were proposed for the purpose of application to a display element such as a fluorescent display device or the like.
For example, when the field emission cathode is applied to a graphic fluorescent display device, electrodes are arranged in a matrix-like configuration to selectively determine turning-on and turning-off of a display section on an anode side of the fluorescent display device. More specifically, in the field emission cathode, any two of an emitter electrode array of the field emission cathode and its gate electrode array and grid electrodes of the fluorescent display device and its anode electrodes are arranged so as to intersect each other, resulting in forming a matrix configuration. When any desired intersections in such a matrix are selected depending on an image to be displayed, electrons are emitted from the field emission cathode in correspondence to the intersections selected and then impinged on phosphors of the anode electrodes, so that selection of picture cells may be carried out.
Unfortunately, it was found that the conventional field emission cathode of the X--Y matrix structure described above has several problems.
One of the problems is that the field emission cathode is driven according to a dynamic driving system, so that its luminous time depends on a duty ratio, to thereby cause luminous time for each of picture cell to be reduced with an increase in the number of picture cells to be scanned, leading to a decrease in luminance.
Another problem is that the dynamic driving system causes a circuit therefor to be complicated as compared with a static driving system.
A further problem is that in the conventional field emission cathode, it is required to form an external circuit, leading to large-sizing of the overall field emission cathode and an increase in manufacturing cost thereof.
In view of the foregoing problems of the conventional field emission cathode, the assignee proposed such an electron source as disclosed in Japanese Patent Application No. 95119/1990. More particularly, the electron source proposed is so constructed that wirings of an X--Y matrix configuration are formed on an insulating substrate and then thin-film transistors (TFT) and field emission cathodes (FEC) are juxtaposed to each other within a plurality of element regions defined on the insulating substrate by the X--Y matrix wirings.
In order to permit a thin film transistor to produce a large current, it is required to increase an area of the transistor. Also, in a field emission cathode using a thin film transistor, arrangement of the field emission cathode on the thin film transistor through an insulating layer deteriorates performance of the thin film transistor; therefore, it is necessarily required to juxtapose the field emission cathode and thin film transistor to each other. Thus, the electron source proposed which includes a combination of the thin film transistors and field emission cathodes has a disadvantage of causing utilization thereof per unit area to be deteriorated.
Further, in the above-described conventional field emission cathode and electron source, the field emission cathode is prepared in silicon (Si) arranged on an insulating substrate such as a glass substrate or the like. Unfortunately, such arrangement causes mobility of electrons to be decreased, resulting in failing to permit the thin film transistor to exhibit desired characteristics.